Glucose activation of the yeast plasma membrane H⁺‐ATPase requires the ubiquitin–proteasome proteolytic pathway

Glucose triggers transcriptional and post-transcriptional mechanisms that increase the level and activity of Saccharomyces cerevisiae plasma membrane H+-ATPase. We have studied the post-transcriptional activation of the enzyme by glucose and have found that Rsp5, a ubiquitin-protein ligase enzyme, Ubc4, a ubiquitin-conjugating enzyme, and the 26S proteasome complex are implicated in this activation. These results suggest that ATPase activation by glucose requires the ubiquitin-proteasome proteolytic pathway. This is supported by the fact that over-expression of the ubiquitin-specific protease Ubp2, which cleaves ubiquitin from its branched conjugates, inhibits this activation. We propose that glucose triggers degradation of an inhibitory protein resulting in enzyme activation.